Conventionally, encapsulation of various substances has been performed in many industrial and technical fields. In the industry of printing, coating material and ink, a large number of encapsulation techniques using a pigment, a coloring matter or the like as the core substance have been practiced. Also, in the medical or agricultural field, many efforts to encapsulate a drug as the core substance have been made for the purpose of increasing efficacy, decreasing toxicity, imparting stability, sustaining the effect, or the like. As for the encapsulation method, a phase separation method (coacervation method), an in-liquid drying method (interfacial precipitation method), a spray drying method, a pan coating method, an in-liquid curing and coating method, an interfacial polymerization method, an interfacial inorganic reaction method, an in-situ polymerization method and the like are known. However, these methods have a problem that, for example, the core substance is limited, the thickness of the shell layer (wall material, that is, coat layer of the core substance) coating the core substance is hard to freely design, encapsulation of one piece of the core substance is difficult, the functional group on the capsule surface is hard to freely design, a particle having a uniform surface state cannot be easily produced, encapsulation on the nano-order is not easy, application to a relatively unstable compound is difficult, a solvent used at the production of a preparation is readily mixed into the product, or the property of the obtained capsule is not satisfied. Also, the resulting encapsulated product itself has a problem depending on the usage.
In an inkjet recording method of jetting out an ink droplet from a fine nozzle head and recording a character or a figure on the surface of a recording medium such as paper, an aqueous pigment ink obtained by dispersing a pigment in water has recently come to be used because of its excellent water resistance or light fastness. As for such an aqueous pigment ink, those obtained by dispersing a pigment in an aqueous dispersion medium with use of a dispersant such as surfactant or polymer dispersant are generally used in many cases. However, when a dispersant is used for the dispersion of pigment particles, the ink composition has many points to be adjusted for ensuring preferred properties as an ink, for example, there is a problem that when high print density, fixing property or scratch resistance is intended to obtain, the viscosity tends to be high.
Furthermore, in such an aqueous pigment ink, the dispersant is merely adsorbing to the pigment particle surface and in the inkjet recording method where a strong shear force is applied to the pigment particle, the dispersant adsorbing to the pigment particle surface is sometimes desorbed, as a result, the dispersibility of the pigment ink may be decreased to deteriorate the ejection stability (property that the ink is stably jetted out to a constant direction from a recording head). Also, in a pigment ink using a pigment dispersed by using a dispersant such as surfactant or polymer dispersant, desorption and absorption of the dispersant readily occurs and when the ink is stored for a long time, the dispersion is liable to become unstable.
On the other hand, for the purpose of enhancing the fixing property of the dispersed particle (for example, pigment particle) contained in a particle dispersion-type inkjet ink (for example, pigment-type inkjet ink) on a recording medium, a technique of using an encapsulated product obtained by coating a dispersed particle (for example, pigment particle) with a polymer is known.
Those prepared by encapsulating a pigment particle (see, for example, Patent Documents 1, 2 and 3) or those prepared by graft-polymerizing a polymer to the surface of a pigment particle (see, for example, Patent Documents 4 to 7) have been proposed. Also, a method of encapsulating a hydrophobic powder by using an amphipatic graft polymer has been proposed (see, for example, Patent Document 8). In these methods, a previously polymerized polymer is used for the encapsulation, and this incurs a problem that a large particle diameter tends to result after encapsulation and the particle diameter cannot be easily controlled.
Other than these proposals, there has been proposed an ink using a pigment on which a resin capable of forming a film at room temperature is coated by a phase inversion emulsification method (see, for example, Patent Documents 9 to 17), or an ink using a pigment on which an anionic group-containing organic polymer compound is coated by an acid precipitation method (see, for example, Patent Documents 18 to 27).
In addition, an ink containing a dispersed particle prepared by encapsulating a color material in a polymer by a phase inversion emulsification method has been proposed (see, for example, Patent Documents 28 to 33). However, when a color material obtained by a phase inversion emulsification method or an acid precipitation method is used for an ink, the polymer adsorbed to the color material may desorb and dissolve in the ink depending on the organic solvent contained in the ink, such as penetrant, and the dispersion stability or ejection stability of ink, the image quality and the like may not be obtained in a satisfactory level.
Patent Document 1:JP-B-7-94634Patent Document 2:JP-A-8-59715Patent Document 3:JP-A-2003-306661Patent Document 4:JP-A-5-339516Patent Document 5:JP-A-8-302227Patent Document 6:JP-A-8-302228Patent Document 7:JP-A-8-81647Patent Document 8:JP-A-5-320276Patent Document 9:JP-A-8-218015Patent Document 10:JP-A-8-295837Patent Document 11:JP-A-9-3376Patent Document 12:JP-A-8-183920Patent Document 13:JP-A-10-46075Patent Document 14:JP-A-10-292143Patent Document 15:JP-A-11-80633Patent Document 16:JP-A-11-349870Patent Document 17:JP-A-2000-7961Patent Document 18:JP-A-9-31360Patent Document 19:JP-A-9-217019Patent Document 20:JP-A-9-316353Patent Document 21:JP-A-9-104834Patent Document 22:JP-A-9-151342Patent Document 23:JP-A-10-140065Patent Document 24:JP-A-11-152424Patent Document 25:JP-A-11-166145Patent Document 26:JP-A-11-199783Patent Document 27:JP-A-11-209672Patent Document 28:JP-A-9-286939Patent Document 29:JP-A-2000-44852Patent Document 30:JP-A-2000-53897Patent Document 31:JP-A-2000-53898Patent Document 32:JP-A-2000-53899Patent Document 33:JP-A-2000-53900